Supported Metal Catalysts: Preparation, Characterization, and Function

Abstract

Abstract The adsorption of carbon monoxide, dioxygen. and dihydrogen on three platinum catalysts (0.89% w/w Pt/alumina, 0.75% w/w Pt/silica, and 0.48% w/w Pt/molybdena) prepared hy impregnation and one catalyst (0.52% w/w Pt/molybdena) prepared by co-crystallization has been studied. On Pt/alumina and Pt/silica, three states of adsorbed carbon monoxide have been detected, one weakly held at 293 K and two strongly held. Of the two strongly adsorbed species, one is linearly bonded, the other bridge bonded. Over 80% of the strongly held material is able to exchange with gas-phase carbon monoxide. On the Pt/alumina, adsorption of submonolayer quantities of carbon monoxide results in a modification of the binding energy of surface hydrogen such that the hydrogen can be displaced by subsequent adsorption of carbon monoxide. Carbon monoxide reacts with hydroxyl groups of the support during thermal desorption from Pt/alumina to form carbon dioxide and dihydrogen. An activation energy barrier was observed for carbon monoxide adsorption on Pt/silica within the temperature range 256-297 K. Pt/molybdena prepared by co-crystallization adsorbed carbon monoxide but not dioxygen.